1) Field of the Invention
The present invention relates to apparatuses and methods for exchanging heat between fluids and, more particularly, to a counter-flow heat exchanger with passages defined by nonplanar sheets.
2) Description of Related Art
Heat exchangers, which are used in numerous applications and industries, generally define two sets of passages that are at least substantially fluidly disconnected. A relatively hot fluid flows through a first set of passages of the heat exchanger, and a relatively cool fluid flows through a second set of passages of the exchanger. The two sets of passages thermally communicate so that thermal energy is transferred from the hot fluid to the cool fluid. The fluids can flow in the same direction, perpendicular directions, or opposite directions. Heat exchangers characterized by opposite flow of the fluids are typically referred to as counter-flow devices.
One application for which the use of heat exchangers has been proposed is gas turbines such as are used in electricity generation. Gas turbines may include catalytic combustors, which generally provide partial combustion of the fuel and air flowing into the combustor of the turbine with low formations of nitrogen oxides (NOX) and carbon monoxide (CO). Acceptable catalytic combustion reaction rates are typically achieved only when operated at a temperature substantially above ambient temperatures. Preburners are sometimes used to heat the incoming airflow via partial combustion, but a prebumer can reduce the efficiency of the turbine, and byproducts such as nitrogen oxides and carbon monoxide can be formed in the preburner. A heat exchanger can instead be used to transfer thermal energy derived from the catalytic combustion process to the incoming air. However, the structural configuration required for such heat exchangers is generally complex. For example, in a conventional heat exchanger for a catalytic combustor, the air enters the heat exchanger in a direction transverse to the primary flow direction of the heat exchanger. In order for the flow direction of the air to be changed in the heat exchanger, the exchanger includes many detailed parts and many internal braze joints that cannot be easily inspected. The assembly of such a heat exchanger is typically labor intensive, and the exchanger is often subjected to large thermal strains that limit the operating life of the device.
Thus, there exists a continued need for an improved heat exchanger device. The heat exchanger should be capable of efficiently transferring thermal energy between fluids, for example, as a catalytic heat exchanger that heats the air flowing into a turbine and for other heat transfer applications. Preferably, the heat exchanger should require fewer detailed or complex parts, and fewer internal joints. The heat exchanger should preferably also be characterized by reduced assembly costs and an increased operating life.